This invention relates to an adaptive equalizer which is used in combination with a demodulator.
A demodulator demodulates a received signal which may be subjected to fading while transmitted to the demodulator through a radio channel. The demodulated signal may be a baseband signal having a binary level or a multilevel. An adaptive equalizer is supplied with the demodulated signal and comprises an equalizer section for equalizing the demodulated signal into an equalized signal in accordance with a main controllable tap gain and first through N-th controllable tap gains, where N represents a positive integer which is not less than one.
A conventional adaptive equalizer further comprises a producing section for producing a main gain value and first through N-th gain values dependent upon the demodulated signal and the equalized signal and a processing section for processing the main gain value and the first through the N-th gain values into the main controllable tap gain and the first through N-th controllable tap gains in accordance with a main parameter and first through N-th parameters, respectively.
The main parameter and the first through the N-th parameters are representative of limiting values for limiting the main gain value and the first through the N-th gain values, respectively. The limiting values are used in rapidly controlling the main controllable tap gain and the first through the N-th controllable tap gains.
The conventional adaptive equalizer is disclosed in an article contributed by Hajime Yamamoto and Takaya Endo to the ELECTRICAL COMMUNICATION LABORATORIES TECHNICAL JOURNAL, VOL. 23 No. 6 of Nippon Telegraph and Telephone Public Corporation in 1974, pages 1115 to 1149, under the title of "Automatic Equalizer in 1.544 Mb/s PCM-FDM System". In the conventional adaptive equalizer, the main parameter is equal to one. The first through the N-th parameters are less than the main parameter.
However, the first through the N-th parameters are not varied in accordance with the demodulated signal in the conventional adaptive equalizer on controlling the main controllable tap gain and the first through the N-th controllable tap gains. As a result, the fading partially remains in the equalized signal. Therefore, it is difficult to effectively remove the remaining fading in the equalized signal.